Correcting the Actual Reproduction Number: A Simple Method to Estimate R₀ from Early Epidemic Growth Data

Abstract: The basic reproduction number, R₀, a summary measure of the transmission potential of an infectious disease, is estimated from early epidemic growth rate, but a likelihood-based method for the estimation has yet to be developed. The present study corrects the concept of the actual reproduction number, offering a simple framework for estimating R₀ without assuming exponential growth of cases. The proposed method is applied to the HIV epidemic in European countries, yielding R₀ values ranging from 3.60 to 3.74, consistent with those based on the Euler-Lotka equation. The method also permits calculating the expected value of R₀ using a spreadsheet.